# working institution:School of Mathematical Sciences,Zhejiang University
# author:Kangjie Ding
# date:2022/11/18 19:52
import pygame
from pygame.sprite import Sprite

class Alien(Sprite):
    """表示单个外星人的类"""
    def __init__(self,ai_game):
        """初始化外星人并设置位置"""
        super().__init__()
        self.screen=ai_game.screen
        self.settings=ai_game.settings
        #加载外星人图像并设置rect属性
        self.image=pygame.image.load("images/cute_alien.jpeg")
        self.rect=self.image.get_rect()
        #让外星人出现在屏幕左上角
        self.rect.x=self.rect.width
        self.rect.y=self.rect.height

    def check_edges(self):
        """检查外星人是否移动到了屏幕两侧边界，如是返回True"""
        screen_rect=self.screen.get_rect()
        if self.rect.right>=screen_rect.right or self.rect.left<=0:
            return True

    def update(self):
        """向左或向右移动外星人"""
        self.rect.x+=self.settings.alien_speed*self.settings.fleet_direction